Commit 6923f6db1e ("malloc: Use current
(C11-style) atomics for fastbin access") caused a substantial
performance regression on POWER and Aarch64, and the old atomics,
while hard to prove correct, seem to work in practice.
This commit removes the custom memcpy implementation from _int_realloc
for small chunk sizes. The ncopies variable has the wrong type, and
an integer wraparound could cause the existing code to copy too few
elements (leaving the new memory region mostly uninitialized).
Therefore, removing this code fixes bug 24027.
The previous check could read beyond the end of the tcache entry
array. If the e->key == tcache cookie check happened to pass, this
would result in crashes.
This commit is in preparation of turning the macro into a proper
function. The output arguments of the macro were in fact unused.
Also clean up uses of __builtin_expect.
On Thu, Jan 11, 2018 at 3:50 PM, Florian Weimer <fweimer@redhat.com> wrote:
> On 11/07/2017 04:27 PM, Istvan Kurucsai wrote:
>>
>> + next = chunk_at_offset (victim, size);
>
>
> For new code, we prefer declarations with initializers.
Noted.
>> + if (__glibc_unlikely (chunksize_nomask (victim) <= 2 * SIZE_SZ)
>> + || __glibc_unlikely (chunksize_nomask (victim) >
>> av->system_mem))
>> + malloc_printerr("malloc(): invalid size (unsorted)");
>> + if (__glibc_unlikely (chunksize_nomask (next) < 2 * SIZE_SZ)
>> + || __glibc_unlikely (chunksize_nomask (next) >
>> av->system_mem))
>> + malloc_printerr("malloc(): invalid next size (unsorted)");
>> + if (__glibc_unlikely ((prev_size (next) & ~(SIZE_BITS)) !=
>> size))
>> + malloc_printerr("malloc(): mismatching next->prev_size
>> (unsorted)");
>
>
> I think this check is redundant because prev_size (next) and chunksize
> (victim) are loaded from the same memory location.
I'm fairly certain that it compares mchunk_size of victim against
mchunk_prev_size of the next chunk, i.e. the size of victim in its
header and footer.
>> + if (__glibc_unlikely (bck->fd != victim)
>> + || __glibc_unlikely (victim->fd != unsorted_chunks (av)))
>> + malloc_printerr("malloc(): unsorted double linked list
>> corrupted");
>> + if (__glibc_unlikely (prev_inuse(next)))
>> + malloc_printerr("malloc(): invalid next->prev_inuse
>> (unsorted)");
>
>
> There's a missing space after malloc_printerr.
Noted.
> Why do you keep using chunksize_nomask? We never investigated why the
> original code uses it. It may have been an accident.
You are right, I don't think it makes a difference in these checks. So
the size local can be reused for the checks against victim. For next,
leaving it as such avoids the masking operation.
> Again, for non-main arenas, the checks against av->system_mem could be made
> tighter (against the heap size). Maybe you could put the condition into a
> separate inline function?
We could also do a chunk boundary check similar to what I proposed in
the thread for the first patch in the series to be even more strict.
I'll gladly try to implement either but believe that refining these
checks would bring less benefits than in the case of the top chunk.
Intra-arena or intra-heap overlaps would still be doable here with
unsorted chunks and I don't see any way to counter that besides more
generic measures like randomizing allocations and your metadata
encoding patches.
I've attached a revised version with the above comments incorporated
but without the refined checks.
Thanks,
Istvan
From a12d5d40fd7aed5fa10fc444dcb819947b72b315 Mon Sep 17 00:00:00 2001
From: Istvan Kurucsai <pistukem@gmail.com>
Date: Tue, 16 Jan 2018 14:48:16 +0100
Subject: [PATCH v2 1/1] malloc: Additional checks for unsorted bin integrity
I.
Ensure the following properties of chunks encountered during binning:
- victim chunk has reasonable size
- next chunk has reasonable size
- next->prev_size == victim->size
- valid double linked list
- PREV_INUSE of next chunk is unset
* malloc/malloc.c (_int_malloc): Additional binning code checks.
The House of Force is a well-known technique to exploit heap
overflow. In essence, this exploit takes three steps:
1. Overwrite the size of top chunk with very large value (e.g. -1).
2. Request x bytes from top chunk. As the size of top chunk
is corrupted, x can be arbitrarily large and top chunk will
still be offset by x.
3. The next allocation from top chunk will thus be controllable.
If we verify the size of top chunk at step 2, we can stop such attack.
This patch mechanically removes all remaining uses, and the
definitions, of the following libio name aliases:
name replaced with
---- -------------
_IO_FILE FILE
_IO_fpos_t __fpos_t
_IO_fpos64_t __fpos64_t
_IO_size_t size_t
_IO_ssize_t ssize_t or __ssize_t
_IO_off_t off_t
_IO_off64_t off64_t
_IO_pid_t pid_t
_IO_uid_t uid_t
_IO_wint_t wint_t
_IO_va_list va_list or __gnuc_va_list
_IO_BUFSIZ BUFSIZ
_IO_cookie_io_functions_t cookie_io_functions_t
__io_read_fn cookie_read_function_t
__io_write_fn cookie_write_function_t
__io_seek_fn cookie_seek_function_t
__io_close_fn cookie_close_function_t
I used __fpos_t and __fpos64_t instead of fpos_t and fpos64_t because
the definitions of fpos_t and fpos64_t depend on the largefile mode.
I used __ssize_t and __gnuc_va_list in a handful of headers where
namespace cleanliness might be relevant even though they're
internal-use-only. In all other cases, I used the public-namespace
name.
There are a tiny handful of places where I left a use of 'struct _IO_FILE'
alone, because it was being used together with 'struct _IO_FILE_plus'
or 'struct _IO_FILE_complete' in the same arithmetic expression.
Because this patch was almost entirely done with search and replace, I
may have introduced indentation botches. I did proofread the diff,
but I may have missed something.
The ChangeLog below calls out all of the places where this was not a
pure search-and-replace change.
Installed stripped libraries and executables are unchanged by this patch,
except that some assertions in vfscanf.c change line numbers.
* libio/libio.h (_IO_FILE): Delete; all uses changed to FILE.
(_IO_fpos_t): Delete; all uses changed to __fpos_t.
(_IO_fpos64_t): Delete; all uses changed to __fpos64_t.
(_IO_size_t): Delete; all uses changed to size_t.
(_IO_ssize_t): Delete; all uses changed to ssize_t or __ssize_t.
(_IO_off_t): Delete; all uses changed to off_t.
(_IO_off64_t): Delete; all uses changed to off64_t.
(_IO_pid_t): Delete; all uses changed to pid_t.
(_IO_uid_t): Delete; all uses changed to uid_t.
(_IO_wint_t): Delete; all uses changed to wint_t.
(_IO_va_list): Delete; all uses changed to va_list or __gnuc_va_list.
(_IO_BUFSIZ): Delete; all uses changed to BUFSIZ.
(_IO_cookie_io_functions_t): Delete; all uses changed to
cookie_io_functions_t.
(__io_read_fn): Delete; all uses changed to cookie_read_function_t.
(__io_write_fn): Delete; all uses changed to cookie_write_function_t.
(__io_seek_fn): Delete; all uses changed to cookie_seek_function_t.
(__io_close_fn): Delete: all uses changed to cookie_close_function_t.
* libio/iofopncook.c: Remove unnecessary forward declarations.
* libio/iolibio.h: Correct outdated commentary.
* malloc/malloc.c (__malloc_stats): Remove unnecessary casts.
* stdio-common/fxprintf.c (__fxprintf_nocancel):
Remove unnecessary casts.
* stdio-common/getline.c: Use _IO_getdelim directly.
Don't redefine ssize_t.
* stdio-common/printf_fp.c, stdio_common/printf_fphex.c
* stdio-common/printf_size.c: Don't redefine size_t or FILE.
Remove outdated comments.
* stdio-common/vfscanf.c: Don't redefine va_list.
malloc_stats means to disable cancellation for writes to stderr while
it runs, but it restores stderr->_flags2 with |= instead of =, so what
it actually does is disable cancellation on stderr permanently.
[BZ #22830]
* malloc/malloc.c (__malloc_stats): Restore stderr->_flags2
correctly.
* malloc/tst-malloc-stats-cancellation.c: New test case.
* malloc/Makefile: Add new test case.
This avoids assert definition conflicts if some of the headers used by
malloc.c happens to include assert.h. Malloc still needs a malloc-avoiding
implementation, which we get by redirecting __assert_fail to malloc's
__malloc_assert.
* malloc/malloc.c: Include <assert.h>.
(assert): Do not define.
[!defined NDEBUG] (__assert_fail): Define to __malloc_assert.
When posix_memalign is called with an alignment less than MALLOC_ALIGNMENT
and a requested size close to SIZE_MAX, it falls back to malloc code
(because the alignment of a block returned by malloc is sufficient to
satisfy the call). In this case, an integer overflow in _int_malloc leads
to posix_memalign incorrectly returning successfully.
Upon fixing this and writing a somewhat thorough regression test, it was
discovered that when posix_memalign is called with an alignment larger than
MALLOC_ALIGNMENT (so it uses _int_memalign instead) and a requested size
close to SIZE_MAX, a different integer overflow in _int_memalign leads to
posix_memalign incorrectly returning successfully.
Both integer overflows affect other memory allocation functions that use
_int_malloc (one affected malloc in x86) or _int_memalign as well.
This commit fixes both integer overflows. In addition to this, it adds a
regression test to guard against false successful allocations by the
following memory allocation functions when called with too-large allocation
sizes and, where relevant, various valid alignments:
malloc, realloc, calloc, reallocarray, memalign, posix_memalign,
aligned_alloc, valloc, and pvalloc.
When the per-thread cache is enabled, __libc_malloc uses request2size (which
does not perform an overflow check) to calculate the chunk size from the
requested allocation size. This leads to an integer overflow causing malloc
to incorrectly return the last successfully allocated block when called with
a very large size argument (close to SIZE_MAX).
This commit uses checked_request2size instead, removing the overflow.
It does not make sense to register separate cleanup functions for arena
and tcache since they're always going to be called together. Call the
tcache cleanup function from within arena_thread_freeres since it at
least makes the order of those cleanups clear in the code.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This commit adds a "subheaps" field to the malloc_info output that
shows the number of heaps that were allocated to extend a non-main
arena.
Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
This patch adds a single-threaded fast path to malloc, realloc,
calloc and memalloc. When we're single-threaded, we can bypass
arena_get (which always locks the arena it returns) and just use
the main arena. Also avoid retrying a different arena since
there is just the main arena.
* malloc/malloc.c (__libc_malloc): Add SINGLE_THREAD_P path.
(__libc_realloc): Likewise.
(_mid_memalign): Likewise.
(__libc_calloc): Likewise.
This patch adds single-threaded fast paths to _int_free.
Bypass the explicit locking for larger allocations.
* malloc/malloc.c (_int_free): Add SINGLE_THREAD_P fast paths.
This patch fixes a deadlock in the fastbin consistency check.
If we fail the fast check due to concurrent modifications to
the next chunk or system_mem, we should not lock if we already
have the arena lock. Simplify the check to make it obviously
correct.
* malloc/malloc.c (_int_free): Fix deadlock bug in consistency check.
The current malloc initialization is quite convoluted. Instead of
sometimes calling malloc_consolidate from ptmalloc_init, call
malloc_init_state early so that the main_arena is always initialized.
The special initialization can now be removed from malloc_consolidate.
This also fixes BZ #22159.
Check all calls to malloc_consolidate and remove calls that are
redundant initialization after ptmalloc_init, like in int_mallinfo
and __libc_mallopt (but keep the latter as consolidation is required for
set_max_fast). Update comments to improve clarity.
Remove impossible initialization check from _int_malloc, fix assert
in do_check_malloc_state to ensure arena->top != 0. Fix the obvious bugs
in do_check_free_chunk and do_check_remalloced_chunk to enable single
threaded malloc debugging (do_check_malloc_state is not thread safe!).
[BZ #22159]
* malloc/arena.c (ptmalloc_init): Call malloc_init_state.
* malloc/malloc.c (do_check_free_chunk): Fix build bug.
(do_check_remalloced_chunk): Fix build bug.
(do_check_malloc_state): Add assert that checks arena->top.
(malloc_consolidate): Remove initialization.
(int_mallinfo): Remove call to malloc_consolidate.
(__libc_mallopt): Clarify why malloc_consolidate is needed.
Currently free typically uses 2 atomic operations per call. The have_fastchunks
flag indicates whether there are recently freed blocks in the fastbins. This
is purely an optimization to avoid calling malloc_consolidate too often and
avoiding the overhead of walking all fast bins even if all are empty during a
sequence of allocations. However using catomic_or to update the flag is
completely unnecessary since it can be changed into a simple boolean and
accessed using relaxed atomics. There is no change in multi-threaded behaviour
given the flag is already approximate (it may be set when there are no blocks in
any fast bins, or it may be clear when there are free blocks that could be
consolidated).
Performance of malloc/free improves by 27% on a simple benchmark on AArch64
(both single and multithreaded). The number of load/store exclusive instructions
is reduced by 33%. Bench-malloc-thread speeds up by ~3% in all cases.
* malloc/malloc.c (FASTCHUNKS_BIT): Remove.
(have_fastchunks): Remove.
(clear_fastchunks): Remove.
(set_fastchunks): Remove.
(malloc_state): Add have_fastchunks.
(malloc_init_state): Use have_fastchunks.
(do_check_malloc_state): Remove incorrect invariant checks.
(_int_malloc): Use have_fastchunks.
(_int_free): Likewise.
(malloc_consolidate): Likewise.
The functions tcache_get and tcache_put show up in profiles as they
are a critical part of the tcache code. Inline them to give tcache
a 16% performance gain. Since this improves multi-threaded cases
as well, it helps offset any potential performance loss due to adding
single-threaded fast paths.
* malloc/malloc.c (tcache_put): Inline.
(tcache_get): Inline.
The malloc tcache added in 2.26 will leak all of the elements remaining
in the cache and the cache structure itself when a thread exits. The
defect is that we do not set tcache_shutting_down early enough, and the
thread simply recreates the tcache and places the elements back onto a
new tcache which is subsequently lost as the thread exits (unfreed
memory). The fix is relatively simple, move the setting of
tcache_shutting_down earlier in tcache_thread_freeres. We add a test
case which uses mallinfo and some heuristics to look for unaccounted for
memory usage between the start and end of a thread start/join loop. It
is very reliable at detecting that there is a leak given the number of
iterations. Without the fix the test will consume 122MiB of leaked
memory.
Clean up calls to malloc_printerr and trim its argument list.
This also removes a few bits of work done before calling
malloc_printerr (such as unlocking operations).
The tunable/environment variable still enables the lightweight
additional malloc checking, but mallopt (M_CHECK_ACTION)
no longer has any effect.
__stack_chk_fail is called on corrupted stack. Stack backtrace is very
unreliable against corrupted stack. __libc_message is changed to accept
enum __libc_message_action and call BEFORE_ABORT only if action includes
do_backtrace. __fortify_fail_abort is added to avoid backtrace from
__stack_chk_fail.
[BZ #12189]
* debug/Makefile (CFLAGS-tst-ssp-1.c): New.
(tests): Add tst-ssp-1 if -fstack-protector works.
* debug/fortify_fail.c: Include <stdbool.h>.
(_fortify_fail_abort): New function.
(__fortify_fail): Call _fortify_fail_abort.
(__fortify_fail_abort): Add a hidden definition.
* debug/stack_chk_fail.c: Include <stdbool.h>.
(__stack_chk_fail): Call __fortify_fail_abort, instead of
__fortify_fail.
* debug/tst-ssp-1.c: New file.
* include/stdio.h (__libc_message_action): New enum.
(__libc_message): Replace int with enum __libc_message_action.
(__fortify_fail_abort): New hidden prototype.
* malloc/malloc.c (malloc_printerr): Update __libc_message calls.
* sysdeps/posix/libc_fatal.c (__libc_message): Replace int
with enum __libc_message_action. Call BEFORE_ABORT only if
action includes do_backtrace.
(__libc_fatal): Update __libc_message call.
MMap'd memory isn't shrunk without MREMAP, but IIRC this is intentional for
performance reasons. Regardless, this patch tweaks the existing comment to
be more accurate wrt the existing code.
[BZ #21411]
* malloc/malloc.c: Tweak realloc/MREMAP comment to be more accurate.
Fixes a typo introduced in commit
be7991c070. This caused
mallopt(M_ARENA_MAX) as well as the environment variable
MALLOC_ARENA_MAX to not work as intended because it set the
wrong internal parameter.
[BZ #21338]
* malloc/malloc.c: Call do_set_arena_max for M_ARENA_MAX
instead of incorrect do_set_arena_test
Additional check for chunk_size == next->prev->chunk_size in unlink()
2017-03-17 Chris Evans <scarybeasts@gmail.com>
* malloc/malloc.c (unlink): Add consistency check between size and
next->prev->size, to further harden against 1-byte overflows.
posix/wordexp-test.c used libc-internal.h for PTR_ALIGN_DOWN; similar
to what was done with libc-diag.h, I have split the definitions of
cast_to_integer, ALIGN_UP, ALIGN_DOWN, PTR_ALIGN_UP, and PTR_ALIGN_DOWN
to a new header, libc-pointer-arith.h.
It then occurred to me that the remaining declarations in libc-internal.h
are mostly to do with early initialization, and probably most of the
files including it, even in the core code, don't need it anymore. Indeed,
only 19 files actually need what remains of libc-internal.h. 23 others
need libc-diag.h instead, and 12 need libc-pointer-arith.h instead.
No file needs more than one of them, and 16 don't need any of them!
So, with this patch, libc-internal.h stops including libc-diag.h as
well as losing the pointer arithmetic macros, and all including files
are adjusted.
* include/libc-pointer-arith.h: New file. Define
cast_to_integer, ALIGN_UP, ALIGN_DOWN, PTR_ALIGN_UP, and
PTR_ALIGN_DOWN here.
* include/libc-internal.h: Definitions of above macros
moved from here. Don't include libc-diag.h anymore either.
* posix/wordexp-test.c: Include stdint.h and libc-pointer-arith.h.
Don't include libc-internal.h.
* debug/pcprofile.c, elf/dl-tunables.c, elf/soinit.c, io/openat.c
* io/openat64.c, misc/ptrace.c, nptl/pthread_clock_gettime.c
* nptl/pthread_clock_settime.c, nptl/pthread_cond_common.c
* string/strcoll_l.c, sysdeps/nacl/brk.c
* sysdeps/unix/clock_settime.c
* sysdeps/unix/sysv/linux/i386/get_clockfreq.c
* sysdeps/unix/sysv/linux/ia64/get_clockfreq.c
* sysdeps/unix/sysv/linux/powerpc/get_clockfreq.c
* sysdeps/unix/sysv/linux/sparc/sparc64/get_clockfreq.c:
Don't include libc-internal.h.
* elf/get-dynamic-info.h, iconv/loop.c
* iconvdata/iso-2022-cn-ext.c, locale/weight.h, locale/weightwc.h
* misc/reboot.c, nis/nis_table.c, nptl_db/thread_dbP.h
* nscd/connections.c, resolv/res_send.c, soft-fp/fmadf4.c
* soft-fp/fmasf4.c, soft-fp/fmatf4.c, stdio-common/vfscanf.c
* sysdeps/ieee754/dbl-64/e_lgamma_r.c
* sysdeps/ieee754/dbl-64/k_rem_pio2.c
* sysdeps/ieee754/flt-32/e_lgammaf_r.c
* sysdeps/ieee754/flt-32/k_rem_pio2f.c
* sysdeps/ieee754/ldbl-128/k_tanl.c
* sysdeps/ieee754/ldbl-128ibm/k_tanl.c
* sysdeps/ieee754/ldbl-96/e_lgammal_r.c
* sysdeps/ieee754/ldbl-96/k_tanl.c, sysdeps/nptl/futex-internal.h:
Include libc-diag.h instead of libc-internal.h.
* elf/dl-load.c, elf/dl-reloc.c, locale/programs/locarchive.c
* nptl/nptl-init.c, string/strcspn.c, string/strspn.c
* malloc/malloc.c, sysdeps/i386/nptl/tls.h
* sysdeps/nacl/dl-map-segments.h, sysdeps/x86_64/atomic-machine.h
* sysdeps/unix/sysv/linux/spawni.c
* sysdeps/x86_64/nptl/tls.h:
Include libc-pointer-arith.h instead of libc-internal.h.
* elf/get-dynamic-info.h, sysdeps/nacl/dl-map-segments.h
* sysdeps/x86_64/atomic-machine.h:
Add multiple include guard.
